Heterozygous, loss-of-function mutations in the BMPR2, ACVRL1 and ENG genes, among others, have been described in familial/heritable PAH (HPAH) and idiopathic PAH (IPAH)9; such mutations are also found in hereditary hemorrhagic telangiectasia (HHT; Osler–Weber–Rendu disease). Here, ACVRL1 is linked to hereditary hemorrhagic telangiectasia.